A connection between the subnets behind the gateways <b>moon</b> and <b>sun</b> is set up
via the gateway <b>carol</b>.
The authentication is based on <b>X.509 certificates</b>. Upon the successful
establishment of the IPsec tunnels, the updown script automatically
inserts iptables-based firewall rules that let pass the tunneled traffic.
In order to test tunnels and firewall, client <b>alice</b> behind gateway <b>moon</b>
pings client <b>bob</b> located behind gateway <b>sun</b>.